Lay summary: Glioblastoma is the most frequent primary brain tumour in adults and is one of the most lethal malignancies. The effects of current therapies are limited and novel therapeutic approaches are urgently needed. The blood-brain barrier (BBB) is a major obstacle in accessing and treating brain tumours through systemic delivery.

Arginine is one of the non-essential amino acids for humans. Normal cells synthesize arginine from citrulline in two steps using the urea cycle enzymes ASS1 and argininosuccinate lyase (ASL). Some human cancers, however, do not express sufficient levels of ASS1 and/or ASL and thus require an exogenous arginine supply. These tumours might therefore be sensitive to Arginine Deprivation Therapy (ADT). We wish to explore if ADT using an enzyme that degrades arginine (ADI-PEG20) can kill brain tumours established in mice. We have established a mouse model of glioblastoma by implanting human tumour cells, intracranial, in the brain of immunedeficient mice. One week after cell implantation, these tumour cells develop human glioblastoma that we can visualise by using bioluminescent imaging which also allows monitoring response to treatments. Next, we have generated preliminary data showing partial tumour response to arginine depletion. We also used a harmless vector based on bacteriophage, bacteria virus, that traverses the BBB to deliver therapeutic genes to tumour cells and achieved partial tumour response. Since glioblastoma patients receive the chemotherapeutic drug temozolomide (TMZ), anyway, we sought to combine our therapeutic strategies, arginine depletion and bacteriophage gene therapy, with TMZ in order to increase therapeutic efficacy. Importantly, our preliminary data show that combination with TMZ significantly increased glioblastoma killing in mice compared to TMZ or bacteriophage alone. additional experiments are needed to confirm the effects of combination of arginine depletion with TMZ or lomustine, which is another chemotherapeutic drug given to brain tumour patients.

The aim of this application is to perform a comprehensive pre-clinical investigation of combination therapies involving TMZ or lomustine with arginine depletion, or bacteriophage gene therapy. We will also combine TMZ and lomustine with the ketogenic diet. The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet that in medicine is used primarily to treat difficult-to-control (refractory) epilepsy in children. Importantly, ketogenic diet has recently been shown to suppress glioblastoma growth in a mouse model of intracranial glioblastoma. The proposed pre-clinical investigation will form the foundation for future clinical trials in cancer patients